Technical Field
Exemplary aspects of the present invention generally relate to a belt assembly including an endless looped belt entrained about a plurality of rollers, and an image forming apparatus, such as a copier, a facsimile machine, or a printer including the belt assembly.
Description of the Related Art
There has been known a color image forming apparatus using an electrophotographic method in which toner images of different colors formed on latent image bearers are primarily transferred onto an intermediate transfer body in a primary transfer process and then onto a recording medium in a secondary transfer process. A secondary transfer device employed in the image forming apparatus of this type is equipped with a belt (i.e., a secondary transfer belt) formed into an endless loop and looped around a plurality of support rollers. A recording medium is interposed between the intermediate transfer body and the secondary transfer belt, thereby transferring the toner image onto the recording medium in the secondary transfer process. This is known as a belt transfer method.
In the belt transfer method, the secondary transfer belt is pressed against the intermediate transfer body by the support roller opposite to the intermediate transfer body to form a secondary transfer nip. In the secondary transfer nip, a secondary transfer voltage is applied to the intermediate transfer body, while the support roller that presses the secondary transfer belt against the intermediate transfer body is electrically grounded, thereby forming a transfer electric field. With the transfer electric field, the toner image on the intermediate transfer body is transferred onto the recording medium delivered to the secondary transfer nip.
Generally, in the belt transfer method, the secondary transfer belt may drift to one side in a width direction of the secondary transfer belt or repeatedly wander back and forth on either side in the width direction of the belt. Such misalignment of the belt (including belt wander) is attributed to dimensional tolerance of parts constituting the secondary transfer device, for example, variations in a parallelism error of rotary shafts of the plurality of support rollers that supports the secondary transfer belt, variations in an outer diameter of the rollers, and variations in the tension of the secondary transfer belt due to changes in the circumferential length of the secondary transfer belt itself.
In order to minimize misalignment of the belt within a certain range, in one example, a flange as a belt tracking member is disposed on both ends of the support roller in an axial direction thereof around which the secondary transfer belt is looped, thereby controlling movement of the belt. In this configuration, as the secondary transfer belt drifts off center in the width direction and reaches the end of the support roller in the axial direction thereof, the end portion of the secondary transfer belt contacts the flange, preventing the secondary transfer belt from moving any further to the side.
However, there is a drawback in this configuration using the flange as the belt tracking member disposed on both ends of the support roller in that the secondary transfer belt creases, hence causing image defects.